This section introduces aspects that may be helpful in facilitating a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admission about what is in the prior art.
In telecommunication systems information is typically exchanged via optical fibers. The most popular transmission formats are SDH/Sonet (SDH=Specification and Desription Language, SONET=Synchronous Optical Networking), OTN (OTN=Optical Transport Network) as defined by ITU-T (ITU-T=International Telecommunications Union-Telecommunication Standardization Sector) and DWDM (DWDM=Dense Wavelength Division Multiplexing).
The optical fibers are used to connect routers or other network elements of an optical telecommunication network. Optical interfaces for these optical fibers are typically located on so-called line cards. Since such network elements are usually intended to interface several other network elements, typically multiple optical interfaces are provided, several of them may be located on a line card. Likewise, one network element can have many line cards.
When such a line card is affected by a hardware failure or even the network element having implemented the line card is affected by a serious hardware failure, typically all optical interfaces implemented on that line card fail along with the line card. While this is acceptable for data traffic that is terminated and/or processed in the particular network element (“terminated traffic”), it is also affecting (i.e. interrupting) all further data traffic that is simply forwarded (“passed through”) by the line card from one of its optical interface to a further one of its optical interfaces. The interruption of this pass-through traffic is a severe drawback that needs to be addressed by additional protection mechanisms. Typically, the network elements are capable of protecting data traffic by means of so-call equipment protection with redundancy when a line card fails, i.e. having at least one additional line card (“protecting card”) already installed in the network element which can take over the function of the line card (“protected card”), or by means of so-called network protection via different ports of the network element when an optical link to the network element fails. Such an additional line card increases system cost and complexity. In case of e.g. IP routers (IP=Internet Protocol) the cost for an additional line card can be in the range of e.g. more than 10.000€. Both protection mechanisms, equipment protection and network protection, are complementary mechanisms which can be applied simultaneously.
In case of telecommunication systems which are very important and which should not fail such as government networks or military networks a higher redundancy is required and therefore, additional optical fibers (“protecting fibers”) may be installed in addition to main optical fibers (“protected fibers”). These protecting fibers may be connected to protecting cards to increase a protection mechanism for the data traffic and which only take over the data traffic when one of the protected fibers or one of the protected cards fails. Such additional fiber connections are expensive as well, especially when going over longer distances, e.g. tens, hundreds or thousands of kilometers.